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Picking a NACA airfoil for a new propeller on a DJI drone?
The idea is to design a fairly simple propeller using Fusion software program that has a CONSTANT airfoil throughout (but that twists or changes in scale as it spans). I want a large coefficient of lift (Cl) to coefficient of drag ratio (Cd). The Reynolds number should be about 28k. Calculated at radius=75% where the blade is most efficient at generating lift. Problem is the airfoiltools.com website shows the Cl to Cd graphs in a way that is not so easy to read. There is also no way to search through the output of the visual graphs. And I imagine scraping a visual thing like a Cl to Cd graph would be complicated. Any help? Regards

This might help

You might consider using OpenVSP.  It can design a much more realistic propeller which you should be able to export to Fusion via  STEP file.

@sophit Propellers have different airfoil requirements than wings. To dreddlord: Start with the NACA 8H12 and see if it does what you need. Use XFOIL to compute the Cl/Cd graphs but be aware that it will not model the centrifugal effects on the boundary layer.

Interesting challenge! The Reynolds number you are in makes for some interesting challenges, specifically that XFOIL (or similar panel method solvers with some viscosity correction and assumptions about flow separation) don't handle well. I think Airfoiltools uses XFOIL data, so I wouldn't necessarily trust it below a Reynolds number of 100k or so (rationale below). Thankfully, someone (Justin Winslow is the name that I know) already did some of the work for you.
He did wind tunnel, vacuum chamber, and CFD studies of different airfoils and rotors for MAV designs in the ballpark of your design Reynolds number. Interestingly enough, something that he quotes at the start of his thesis is an figure (below) from a NASA Langley article.

The point of it is that, when we get down below a Reynolds number of 100k, air starts acting very differently from how we are used to in the model airplane (I'm thinking your typical 3D acrobatic RC planes, not peanut scale rubber band models) or even the smaller of the manned aircraft world. One result of this is that NACA airfoils (and anything in that general shape) behave much worse. When you look at a Reynolds number in the 20k-30k, the blunt leading edge of a typical NACA airfoil (such as the NACA 0012 in the figure below) aggravates the adverse pressure gradient on the airfoil and leads to early trailing edge flow separation. The separation bubble on the top of the airfoil effectively increases the thickness of the airfoil and dramatically decreases its L/D. Ironically, if you flip around the same airfoil (such that the traditional trailing edge faces into the freestream), it actually performs better! You still get a separation bubble for a given angle of attack (because of the sharp turn the air must make at the new "leading edge"), but, since there isn't a blunt face at the front of the airfoil, it is much smaller.

With flow separation being such a concern and having such a dramatic effect throughout an airfoil's expected performance region, it is necessary to be able to predict it well. XFOIL, being, at its core, a panel method solver, uses the e^n criterion for estimating the transition point between laminar and turbulent flow. The exponent is chosen based on application and is usually accepted as n = 9 in most cases. However, this assumption breaks below an Reynolds number of 100k, and becomes incredibly difficult to accurately set without another set of data guiding the correct selection of n. As a result, for cases below a Reynolds number of 100k, the selection of n is highly variable and, as a result, a large source of error when using XFOIL to predict airfoil performance parameters in this flow regime. We'll stick with TURNS2D (the code validated in Winslow's thesis for use on low Reynolds number problems like this) and experimental results from here on out.
Looking back at our TURNS2d results, let's take this idea of thinner leading edges being better to its logical conclusion, it means that the thinner your airfoil, the better it will do (aerodynamically, at least). To this end, Winslow 3D printed some 1% thick (essentially flat plate) airfoils with varying amounts of camber, and they outperformed a NACA0012 foil dramatically. Naturally, too much camber gets you into the same issues with flow separation and increased profile drag, but a 3-6% camber on a flat plate airfoil seemed to produce excellent results.

You can also see this in the density contours shown below. Note the variation in size of the separation bubbles for the flat plate vs NACA0012.

Naturally, the follow-up question is whether or not you could just use a thinner NACA foil, and the answer is yes. CFD results from TURNS2D indicate that 3% thick NACA foils can have similar performance when compared to cambered flat plates at similar Reynolds numbers (note: the larger L/D values on this plot are at Re = 100k, whereas the dashed lines are at Re = 20k), although, given the resolution of a 3D printer on the scale you are likely working, I'm not sure how much of an actual NACA profile could be reproduced.

And thus the last item here is actual design and production. Winslow successfully printed his rotors using soluble support materials and had very low design loads: as a result, he didn't need to add reinforcement. The DJI's of the world appear to use a similar design philosophy in their newer rotors (cambered, thin airfoil), but everything is injection molded plastic. Your greatest limitation will likely be your manufacturing method. To this end, it may be helpful to read this as well.

hi there Marius, very interesting comment. You were right, my biggest limitation was my manufacturing method. I have however actually finished this project over 6 months ago and already graduated having written a project report and given an oral presentation to my classmates which passed thankfully. But thanks for your interest.

Regarding tools:

Digitizing data from plots is feasible, but it requires human effort.
The Airfoiltools website utilizes Xfoil, a free software that enables you to generate the necessary data (CL/CD) with any geometry. It may take some time to become accustomed to it.

Regarding the design-process:

Commercial drones are already optimized for a specific mission profile. If you need to increase the performance, be aware that you may hit other bottlenecks (battery, motors, software, controller, propeller clearance, etc).

Assuming you're going to 3D-print the propellers, remember that you'll also have structural/mechanical constraints.

A basic testing bench might help more than Xfoil and the optimization process you may try, if you have not designed propellers before.

If this is a class-work please share your current work and approach a bit more.
Tip: Comparing best CL/CD ratios is simple with human eye, or taking note of the top-left-most point and writing its CL and CD figures down.


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Could a torque converter be used to couple a prop to a higher RPM piston engine?
Every RPM reduction gearbox I look at seems to have more parts in it than a Swiss watch.  Great for keeping time but many parts to wear and breakdown.
What seems especially worrisome is the direct coupling of the engine drive shaft, through the gear, to the prop.  This seems fine when the engine is turning the prop, but potentially damaging if the prop starts turning the engine.
The torque converter, with it hydraulic coupling, seems to offer a safer approach because the prop is not directly connected to the engine power output shaft.
Hydraulic torque converters are commonly used with automobile automatic transmissions.  Are any aircraft using them?
As smaller, higher RPM engines become more common, is there a chance they will be a market for them in aviation?

That's basically a free-turbine turboshaft engine, where the coupling medium is gasses.

@user71659 So I have heard.  Could a piston engine try it?

You are looking at mechanical devices that convert the torque of an electric motor into the rotation of a propeller. Is it possible to use the current mechanical system and solve problems (or at least minimize their impact) by developing a special motor control system?

@dtn Flexidynes can be used on any driven system.  Your question could be posted as a follow up.

"What seems especially worrisome is the direct coupling of the engine drive shaft, through the gear, to the prop". Are you sure about that? At least in the helicopter world there's always a freewheel inbetween.

@sophit apparently, other people worry about that too.  Helicopter free wheels allow auto rotation without (failed) engine drag.

@sophit you could use a sprag clutch to deal with resonance peaks, although it may wear on the sprag rollers. Main problem though is you don't want the propeller to free wheel with no power to it. It turns into a massive speed brake, even if it doesn't overspeed windmilling.

@JohnK: thanks for the clarification

"potentially damaging if the prop starts turning the engine." -- I don't think this is universally true.  I believe it was true for some large radial piston engines, but is now something of an old wives tale when applied to all piston engines.

Fluid torque converters would fix the torsional resonance problems on gear reduction systems, but they are inefficient (significant power losses) and fairly heavy.
When Molt Taylor designed his flying car, the Taylor Aerocar, which the FAA (nee CAA) certified as an aircraft in the early 50s, it used a Lycoming O-320 for power, and to deal with the long drive shaft, which has similar torsional resonance problems as a gearbox, he went with the Flexidyne Dry Fluid Coupling. They are still widely used in industrial equipment and appliances like washing machines.
The flexidyne is a housing filled with small balls (steel shot) and the output shaft is driven through a wavy plate buried in the ball bearings. When it spins, the ball bearings become semi solid from centrifugal force, with just enough give to create a compliant energy absorbing drive transfer with much more efficiency than a fluid torque converter.

Yes, indeed!  See the Lesher Nomad.

They get hot in this application because the steel shot is constantly being displaced tiny amounts on every power pulse during a resonant phase.  I think you still need to mitigate it as much as possible in design (drive shaft stiffness, gear lash tuning etc, so the Flexidyne only has to work through resonant RPM bands you avoid continuous operation in.

In addition to John K's answer there is one more consideration: the heat the torque converter produces. Cars run at about 15% "power setting" when cruising, airplanes run at about 75%. TC will run hot at these conditions, especially since a TC lockup can not be used since this bypasses the TC.
Cooling would have to be arranged, adding complexity / points of failure, and weight to the system.

@Jpe61.You are right about the heating issues. Cars use "lockup" to improve fuel economy.  But I am sold on looking into the Flexidyne, and I think the Lesher Teal could fly off vs the Rutan Vari-eze.

Note that current Flexidyne couplings are not meant to run on constant slippage. They are soft start / overload protection.

@Jpe61 yes IIRC they got quite hot when Taylor used them in the Aerocar and Mini IMP if the resonance problem was severe, so you have to mitigate resonance problems as much as possible and use the Flexidyne to trim off the last bits.

Neither the Flexidyne coupling nor a locked-up torque converter do any torque conversion, and so do not offer an alternative to gearing for matching a higher-speed engine to a lower-speed propeller.

Hence the phrase "...TC lockup can not be used since this bypasses the TC..."

@sdenham RPM reduction is accomplished by gearing.  Matching a high speed engine to a low speed propeller is simple gearing.  A fluid coupling would act as a "shock absorber", preventing anything that happens with the prop from damaging the drive train.  Think about it with cars.  Your engine/trans has momentum.  What would happen if you slammed on the brake?

@RobertDiGiovanni It is not clear to me what point your question is  relevant to. The question’s title asks about coupling a propeller to a higher-RPM engine, and its body expresses a concern for the complexity of reduction gears. I feel my comment is relevant to this issue, but what, in aviation, is analogous to slamming on a car’s brakes? Maybe landing wheels-up and striking the propeller on the ground?

@RobertDiGiovanni On reflection, it seems that you are unaware that hydraulic torque converters, unlike simple fluid couplings, do perform torque amplification, with a corresponding reduction in RPM, like reduction gears, though less efficiently and only over a limited range of ratios. This is accomplished by having a third set of vanes, attached to the stator rather than either the input or output shafts.

@sdenham it boils down to weight and reliability.  Would avoiding potential stresses from pitch change or excessive engine torque (on a rigid drive shaft) by using a TC lead to a lighter design? But I am hearing your distinction of TC vs fluid coupling.  Ideas are evolving.

@RobertDiGiovanni This is bizarre: your question is explicitly about using TCs for matching RPMs, yet in your replies to me here, you are talking about using gears for RPM reduction and fluid couplings for stress reduction! Given that your original question already has replies, you should probably raise these new issues in a separate question.

Slamming the brakes on a car with traditional clutch will stall the engine. A small amount of slippage in the clutch and the brake will prevent shock loads from reaching infinity.

Just as @sdenham wrote torque converters by definition alter the torque. A fluid coupling is a different device. When deciding which damping application is best for a specific case, a lot of variables need to be taken into consideration. Transferrable peak torque and torque range, frequency and amplitude of vibration, time scale, acceptable losses, mtbf, serviceability, etc. etc... My more than less educated guess is, that if torque converters were suitable for aviation applications, they surely would be widely used by now.

Too all, thanks for your inputs, not as bizarre as much as getting better focus.  I simply will not accept "if it were a good idea somebody else would have done it already".  BTW, cars do not stall when brakes are applied unless they are old style manual transmissions with foot clutches. (I drive a 10 speed semi with one).  And yes, having learned more, a reduction gearbox and a (lockable) fluid coupling is more what I'm after if there is a need.  One comment said prop stress dangers were "old wives tales" from radials, and another (from the jet age maybe) said engines cause the stress.

But, again, reducing stress loads with what essentially is an engine/prop load shock absorber still seems of interest.  Another story I heard was a trainee downshifting to 3rd instead of 8th.  Little bit of stress there.  Same if pilot goes full feathered instead of making pitch finer?  Imagine the stresses on the engine mounts!

Stresses from skipping gears on a semi do not compare to stresses  caused by prop pitch (mis)management, not even close. Air is a compressible fluid medium, so it acts as a very good damper itself. The torque pulses from the engine are another thing, of course. You can shear gears or splines, pop u-joints and twist axles pretty effortlessly on a high torque land vehicle, not so much on an aeroplane. As for the clutches and stalling the engine in modern vs. the olden days, I specifically mentioned "traditional" clutch in my previous comment

@Jpe61 OK, I'm buying these days the engine (particularly (piston) torque pulses) may be more of an issue.  Good reading here.

I recently explored each of the available methods used to couple high RPM engines to low RPM propellers. Takeoff HP, Cruise HP, Gross weight, Propeller mass and circumference, and aircraft maneuverability are critical issues. All these have an exponential relationship with forces, some squared, some cubed.
Now, back to your original question; it is a great question. If you try to reduce speed via a torque converter, you'll have to use the type that exchanges fluid with an external cooling radiator. I didn't calculate the size, fluid volume, exchange rate, etc. because I didn't intend to reduce RPM this way.
To reduce speed via the TC, there would be much engineering effort, although mostly dealing with the heat rejection system. My design is 300HP in RV10... I dismissed the TC idea early because the heat rejection system would be far too large, heavy, and risky. If you were working on something 100HP or less, and maybe half the weight, without aerobatics, it could be plausible enough to work on rough calculations.
A typical torque converter where RPM out = 65% of RPM in, would be 85% efficient, so the other 15% will be heat. So propeller horsepower from 100HP engine would be 85HP. And you have to get rid of about 12kW continuous heat. When you consider belt or geared drives will be 98-99% efficient, TC speed reduction is unpopular.

automotive torque converter designs solve efficiency issues with the ability to "lock" the converter in cruise.  Some have pointed out that a turbojet turbine is essentially a torque converter using the exhaust as a fluid medium.  Ah, yes, about the efficiency, pistons remain higher, and are heavier, jets maintain thrust at higher airspeeds. But true, automatic transmissions can get hot.  But one might wonder if a fluid coupling/radiator is heavier than a gearbox.  Which one would be more prone to breakdowns?

In the locked position, there is very little heat, and very little loss, and RPM in = RPM out. I inferred from the original question the intention is to use only a TC to reduce RPM. If input <> output, the converter cannot be locked. Auto trans are planetary gear systems which are very efficient. If you use a TC to drive a planetary reduction, you still cannot lock the TC, because you loose the decoupling of engine pulses. I checked my calcs for 300hp, @18k ft. was min. 16" dia. at 107lbs for TC alone. Now add pump, radiator, liquid, lines. In my notes I noted 100lbs for a gear box +misc.

A turbojet is not a TC. It is a jet engine combustion chamber which scavenges exhaust gas inertia with a turbine directly coupled to an intake compressor via a center shaft. Better described as a turbocharged jet engine. Torque is torsional force applied to a rotating body. A TC has a mechanical rotating input driver and mechanical output. The input impeller accelerates fluid from center to circumference, the turbine decelerates this fluid from circumference to center. The fluid is returned to the impeller through the stator, which changes its direction. Entirely different than turbojet.

As for reliability, the question is far too general to answer well. If we assume the quality of engineering and development are equal, I can definitely answer. In my experiences, poor efficiency machines always suffer early failures. All the energy lost from in to out must be disposed of as heat, noise, etc... It's very handy the coupling fluid is also the cooling fluid. All the metal surfaces contacting fluid are coolest. Trouble is, the core of the same metal is warmer. This dynamic strains and releases each cycle causing fatigue failures within the material. Higher heat equal earlier fail.

Are "planetary gears" needed for RPM reduction?  Starting to wonder if two different size pullys and a slip clutch would work.  Had on of those on a go-cart as a kid.  I'm most interested in using theTC to save strain on the drive when changes are made to the prop, then re-locking it.

No, any speed reduction mechanism will reduce the speed. There are pros and cons to each type of device. There is so much engineering involved here. Many have failed, many are dead. They all were so proud of their machine, then drilled it into a smoking hole. You are thinking backwards. It is mostly the engine causing all driven components to fail. It will break every prop blade, hub, gear box, shaft, even the engine mount. There are many types of belt drives, characteristics vary. A nice damper, small, light, no speed https://aftermarket.schaeffler.us

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Why is the center of pressure of a rocket at its centroid?
From thin airfoil theory, at subsonic speeds, the center of pressure of any uncambered airfoil is at quarter chord. For sounding rockets, however, the center of pressure is generally assumed to be located at the centroid of the projected area. Note that model sounding rockets generally stay subsonic.
What is the theoretical derivation for this? For this question, one can ignore the effect of fins and restrict to the axisymmetric slender bodies.

Just FYI, you're more likely to get answers on questions like this at Space.SE

Isn’t the aerodynamic center at the quarter cord and the location of center of pressure changes with AoA at the airfoil. https://aviation.stackexchange.com/a/19399

@kolom For symmetric thin airfoil it stays at quarter chord

This answer may not be what you are looking for, but I think the issue is we aren't really talking about the rocket as a "wing" here since these rockets fly ballistically.   I think the term CP in the NASA article would be better expressed as "neutral point", the point at which aerodynamic moments are in balance when the rocket is not aligned with the airflow, taking into account the body and all of its appendages.
So this would include the fins as part of the total lateral area subject to lateral air loads when the rocket yaws while flying ballistically, and to be stable, the rocket's center of mass needs to be forward of the neutral point, so that when it yaws, the corrective moment, acting at the aerodynamic neutral point, is created about the center of mass to bring it back into alignment with the airflow.
The term CP suggests that the rocket is flying like a lifting body wing, with a constant angle of attack and lift being generated to support its weight.  But as a ballistic object, its AOA is always ideally 0 and what lateral aerodynamic forces are being created are strictly to keep the rocket's tail lined up behind its nose as it travels its ballistic path.

Restricting the discussion to the body only, just as in aircraft, the definition of neutral point is identical to aerodynamic center. That is, the point where the pitching moment is invariant with flow incidence. If your CG is ahead of the AC, and the Cm at AC is zero at zero incidence, then you have stabilized flight at zero incidence. The difference is, it is mentioned by various sources that CP is relatively constant for rockets (perhaps only for small incidences), so CP and AC coincide and there is no differentiation.

Thanks for the link, we may need to break out the old NACA films and do some refreshment for the benefit of NASA.
After correctly explaining the center of pressure would the sum of pressure of the nose, fuselage, and tail, they proceed to the "simplified" version of "hang a 2 dimensional cutout  from a string".  I think I'd rather try my office fan out as a crude wind tunnel!
The rocket pictured in the link has large fins, which as cruciform "horizontal and vertical" stabilizers give the rocket directional stability. Thrust(lift) is from the rocket engine.  It path is straight up, it does not use any part of its body for lift, nor does it have a wing.  The center of drag (the rocket is symmetrical) is right in the middle of the nose looking directly at the FRONT of the rocket.
The fins give it directional stability, and moving CG towards the nose more so.  But remember, directional stability from fins is AERODYNAMIC,  so we put it on a launch rod so it has speed before it flies free.  (F-16s launching Sidewinders at 400 knots do not have this issue)
Now, as in aircraft, let's move on to side forces. Here is where center of pressure analysis
becomes applicable.  A crosswind will weathervane a rocket just like an airplane. So now you decide how much weather vaning  you want, trading a little directional stability for less weather vaning, or like the US Army did with their Nike Hercules, putting fins on the second stage too.  This gives resistance to gyrations of the fuselage (caused by a lack of fins and imperfect thrust vector), and it worked because the Hercules was guided.  This forgotten "cold war" relic may have been the best airplane the Army ever made.
But for a non-guided directionally stable model rocket there will be some weather vaning in a cross wind.  A possible solution would be thrust vectoring, or add some finnage to the nose to reduce it to acceptable levels (and remaining directionally stable).
Cutting out a 2 dimensional shape (of consistent thickness) ignores the effects of wind on a larger width tail area, though any error would be in favor of stability.  It is surprising that NASA would not encourage young modelers to understand aerodynamic stability.  Firstly, explain "centroid" as the center of AREA.  Next explain for flat plate stabilizing effects (as compared to airfoils), that is where the Center of Pressure is because .....
Finally, scaring people off by saying it is all complicated calculus?? No, a simple side force wind tunnel and a string works fine.  Set the rocket upright and apply aerodynamic side force with a fan. Attach the string to one point and see if it tips over.  Keep trying until you find CP.

So why is the center of pressure of a thin body located at its hydrostatic center? You haven't explained any of it, which is my question.

Sorry, I meant centroid.

We may be looking at flat plate lifting characteristics.  Since a thin airfoil may lose top lift after a few degrees AOA and behave like a flat plate (or a stalled airfoil), CP would move to the center.

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Can commercial automatic flight control fly back-side?
For most commercial flight director, autopilot and auto-throttle systems (e.g. the A330-300, B737-800), the flight director/autopilot flies the altitude hold (ALT) or vertical speed (V/S) mode by closing the flight path/altitude loop with pitch control, while the auto-throttle maintains airspeed. It's only in flight level change (FLC/CLB/DES) or go-around (GA) mode that the autopilot controls airspeed via pitch control and the auto-throttle controls a thrust rating.
Closing the loop around airspeed via throttle and closing the loop around flight path via pitch control work fine when the aircraft is on the front-side of the thrust curve. However, this control strategy leads to instability when flying on the back-side. While this scenario is not likely to be encountered in normal flight operations, the best climb speed for maximum weight would be pretty close to the boundary (with some margin built in by the manufacturers).
How do the automatic flight controls handle flying on the back-side? Or do manufacturers ensure that the floor speed/AOA for system engagement always have margin to the minimum drag?

You can easily find yourself on the back side if you are cruising at or near service ceiling with not a lot of margin above Min Drag speed, and unwittingly fly through some smooth descending mountain wave, where the only indication is a very gentle pitch up as ALT mode corrects to hold the altitude, with speed also gently bleeding off. Don't catch it in time and you have no choice but to descend. Very intriguing question.  The only autothrottle I've flown was an STC add on to a corporate CRJ, and it had a speed mode independent of a/p ALT hold, so it would react w a thrust increase on its own.

Fly-by-wire comes most of the time with protections that try to avoid abnormal flight conditions. Yet, autopilots are designed to disconnect and give control back to pilot when not able to handle a situation.

@ManuH That's part of my question: does it disconnect? Some A/T (like the A220, A3X0 varieties) have floor features that push thrust when AOA/airspeed below critical, but that's provided the A/T is engaged. As far as I know, A/P does not automatically disengage unless you have unusual attitudes or stick shaker.

@JZYL my understanding is that protections are not part of Autopilot. They are here whatever the input source (pilot and/or autopilot) but in some cases autopilot disengages but there is no link with flight envelop protection. Note that the AF447 autopilot disengages when loosing reliable dynamic pressure reading (and also lose part of its flight envelop protection at the same time). So I'll guess autopilot will disengage in all situation it is not designed for.

@ymb1 This accident is quite different from my question. This accident is a result of unannunciated sensor degradation and crew's failure to monitor airspeed. My question assumes all systems are functional.


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Maneuvering Speed and load factor at different gross weights/ configurations
Many aircraft POH documents list Maneuvering Speed, and as is appropriate, they include a caveat that this speed is calculated at maximum aircraft gross weight. They then, often, include a second Maneuvering Speed at a lower gross weight, using the fact that at lower gross weights, the maximum available Angle of Attack can produce the same maximum load factor (as defined in the POH), at a lower calibrated airspeed. This is of course true. Load Factor, (G) is Lift / Weight, and there is no Weight variable in the Lift equation.  Maximum allowable Load Factor changes as gross weight changes, yes, but does maneuvering speed?
Load factor, (acceleration or Gs), does not break anything, it is local stress on a piece or section of a structure (like an airframe, or wing), caused by an applied force, which causes that piece or section of the structure to fail. At any airspeed, at the critical AOA, regardless of gross weight, the aircraft aerodynamics will produce the exact same total aerodynamic force, (and therefore the same total lift force). The G's will of course be higher if the gross weight is lower, but the Lift produced, and the forces on the airframe, will be the approximately the same.
There will of course be small changes due to differences in the distribution of the total force - the local forces on various parts of the airframe due to changes in the force distribution pattern. Obviously, burning off all the fuel in the wings spreads the total mass of the aircraft more evenly along the main wing spar, and this reduces the local stress on each point along the spar. (This is why they put tip tanks on aircraft).
As an aside, other things significantly affect this as well. Rolling the aircraft changes the lift distribution pattern, putting higher stress on parts of the up-moving wing than on the downward moving wing. This is why military aircraft have lower rolling G-limits.
So maneuvering speed, (which is ostensibly based on the risk of structurally damaging the airframe due to an inadvertent gust or updraft/downdraft, etc.) causing an AOA excursion close to the maximum critical angle of attack, should be the same, (or nearly the same) at all gross weights. Sure, at a lower gross weight, that same excursion will result in higher G-load, but the aerodynamic force, (F=ma), and the resultant stress on the airframe, will be the same.
here for example is a chart from the F-4E flight manual, that clearly illustrates that Load factor limits are dependent on gross weight.

Why is it a common practice to list a lower maneuvering speed for lower gross weight conditions on GA aircraft POHs?? I was surprised recently to see an You Tube video which mentioned this (not as causal) in the process of analyzing an accident.
Is this done simply based on the mistaken (Appeal to Authority) argument that once the manufacturer or FAA certification authority has defined and published a maximum load factor for an aircraft, that that published load factor must be utilized and respected for all flight conditions and analyses?

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Because the maneuvering speed is not calculated to safeguard against pulling the wings off the fuselage (or vice versa depending on how you look at), or to limit the bending load applied to wing spar.  The maneuvering speed is calculated to prevent large heavy items of fixed mass from being ripped off their mountings.  E.g. the main electrical battery, the engine(s), etc.  Limit the G-load, and you limit the stress on these mounting points.
As far as the wing-to-fuselage junction goes, or the bending load applied to the wing spar, adding additional weight to the fuselage obviously cannot be protective, and the maximum G-load that these structures can tolerate clearly decreases if extra weight is added to the fuselage.  But not if extra weight is added to the wingtips.
See also these answers to related ASE questions:
Why does maneuvering speed vary with weight?
How does an aircraft's weight affect the V-n diagram?
G Load during payload drop
What is Vg in this VG diagram?

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Imagine the forces on just the engine during a 4g pull-up. We'll assume the engine is at idle for simplicity. The engine is accelerating upwards at 3g just like the rest of the airplane. This requires the airframe to exert a force of four times the weight of the engine to produce this acceleration.
Thus, the force applied to the engine by the airframe is a function only of load factor, and the total weight is irrelevant. If the attachments of the engine to the rest of the airframe are the weakest link, then the maximum load factor is not a function of total weight and the maneuvering speed will increase with gross weight.
This isn't how it has to be in every aircraft. It may be that the some part of the wing is the weakest link. This would manifest as mostly-fixed maximum total force and a decrease in maximum load factor with increased weight, which leads to a maneuvering speed that does not change much with gross weight.

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How to compute thrust to weight ratio of a Cessna 172?
Cessna 172 has weight about 1 ton and it's engine produces about 213 Kg of thrust, and it flies great.
So if I make a plane with a weight of 100kg including pilot and fuel so will 15 kg thrust good for the plane, and if not please recommend me engine which is perfect and please also recommend me the best prop size.
What is thrust to weight ratio of Airplanes.
Sorry for bad English. thanks

The kilogram is not a unit of force, but of mass...

@xxavier you know units in aviation are confusing. Forces are often expresseed in Newton, often in lbs. length are in foot for altitude, meters for visibility, Nm for range. pressure in hPA or in inHg depending on location,... I think aviation people like to confuse others (I see no other reasonable explanation)

@ Manu H You're right... Even in 'metricated' countries, there are still people that use the kilogram (strictly speaking, kilogram-force or kilopond) as a unit of force. No problem there, provided that when a mass is involved, it should be reckoned in the obscure 'mass technical unit', sometimes termed 'hyl', TME, UTM... If someone insists in also using kg as a unit of mass within that context, the constant 9,8 must be present...  All that is a mess, a source of errors, and fortunately, the 'technical units system' is today almost dead...

You can see, from this picture, that in straight and level flight, the drag D is equal to the thrust T. You can see, also, that the lift L is the same as the weight W.

So you can easily calculate the value of thrust T, provided that you know the L/D of the whole aircraft for a given airspeed.
If, for example, that L/D is 9 for an airspeed of 35 m/s (as in many ultralights), and the mass of the airplane es 350 kg, then the thrust will be:
350 x 9.8/9 = 381 newton, where that 9.8 is the acceleration of gravity in m/s/s
.

So as not to confuse, the "weight" of the plane must be in Newtons as well, to generate a "ratio".  But yes, expressing thrust in "lbs" is "old school".  For your plane, the ratio is about .11 for level flight.

In SI units, weight is always expressed in newton, because it's a force... Drag and lift are obviously forces too, as is  thrust, and they should also be reckoned in newton, within the SI.

A good estimate for a personal aircraft thrust requirement would be more like 25% of aircraft weight, and remember, the "ton" of Cessna includes fuel and pilot too!
So: 1 ton x 2000lb/ton x 1kg/2.2 lb = 909 kg Cessna
213 kg thrust/909 kg weight = 23.3 % thrust to weight ratio.
But a lot depends what your plane design is.  You can test thrust requirement for level flight by gliding, then multiplying weight x altitude lost/distance flown = thrust.
So it helps a lot to have a good, strong wing too, and more thrust will be needed to climb.  15 kg may not be enough for your plane, but as long as you are on internet, you may wish to study "ultralight aircraft" to get some better information.


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What is the name of the Instrument that indicates roll?
What is the name of the instrument that would indicate whether the wings are level or tilted (one higher than the other) as when flying IFR? Is it the inclinometer?

The only1 instrument that directly indicates the bank angle is the attitude indicator, also (especially formerly) known as the "artificial horizon".  As another answer has noted, many other instruments give indirect indications of bank angle, and by using them appropriately, it is quite possible to keep the wings level even with no direct indication of the bank angle.
The magnetic compass (even of the simple "wet" type) could be added to the list of instruments that indirectly indicate bank angle, though its use is very limited.  (For example, at mid-latitudes in the north magnetic hemisphere, it is generally not feasible to rely solely on a magnetic compass for bank attitude control, even in very smooth air, on headings that lack a significant southerly magnetic component.)2  It would be very challenging to use a magnetic compass to keep the wings level in any significant amount of turbulence, even if the pilot were free to choose a target heading that gave optimal perfomance of the compass.
The inclinometer doubles as a bank angle gauge if the aircraft is kept on a linear flight path.  Since any deviation from wings-level flight generally causes the flight path to curve, the inclinometer is of no practical value for keeping the wings level in clouds.
Beware of the term "turn and bank indicator".  This is another name for the needle-and-ball turn rate indicator, or its vintage British equivalent that has a second pointer arm in place of the ball.  But the ball-- also known as the "inclinometer"-- or the second pointer arm-- really just indicates sideslip, not bank angle.  As noted above, only if the flight path is constrained to be linear does the inclinometer reading correlate to the bank angle, and that is not a realistic constraint for most cloud-flying situations.  A better name for this instrument is "turn and slip indicator".  A more common name in modern times for this instrument is simply "turn rate indicator", with the fact that a slip-skid ball (inclinometer) is mounted in the same housing going unmentioned.
Footnotes:
1-- Here's a notable, but rarely-seen, exception to this statement-- the "Bohli" compass is a specialized compass for use in gliders.  One of its many advantages over a more conventional magnetic compass is that it provides some direct indication of bank angle.  See these related ASE answers for more about it-- How can pilots fly inside a cloud? , Is it normal for gliders not to have attitude indicators?
2-- Same as footnote 1!

Many instruments can indicate roll. Here is a list in order of Primacy according to the Primary-Secondary Method of Instrument Flying:

Heading Indicator
Attitude Indicator
Turn Coordinator
Rate of Turn Indicator (when TC is absent)
Inclinometer (actually only measures coordination)

In the Control-Performance Method of Instrument Flying, and what most pilots use for real world flying, the Attitude Indicator is used to measure bank angle. Caution should be used at extreme pitch and bank angles. A gyroscopic AI can tumble at angles past 60°, making it unreliable past that.

I would not deduct bank angle from heading indicator alone. It tells you whether your heading is changing or not, but it is not necessarily doing so due to bank angle. You can also fly dead straight with 90 degree bank angle ;)

Hi, thanks so much for your answers. I am writing up an incident that occurred in 1969 involving a Beechcraft D-18 originally owned by the Royal Candadian Air Force and probably not changed much if at all since it was built. The instrument I want to name gave a direct, visual indication of the plane's wings relative to level, so based on your answers I believe it was An Attitude Indicator. Do you happen to know whether it would have been called an Attitude Indicator in 1969? Or an "artificial horizon"?
Glenn

@Glenn - Hey, Glenn. You will need to find a POH, AFM, or owners manual to get the exact nomenclature for that make, model, and year. Take into consideration that the avionics might have been changed out since it’s build date.

Thanks. I think for my purposes "Attitude Indicator" will do.


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What is the limit between lower and higher airways in VFR?
On skyvector you see "World high", "world low" and the VFR map.
VFR is always under the clouds, correct?
But how high do you have to be to follow the high/upper and how high for the low/lower airways?

I reworded the title so that it is more specific. Feel free to reword it if it doesn't fit your question (I may have misunderstand your question)

Skyvector uses official charts from the US National Aeronautical Chart Office (NACO) where available. For the rest of the world, it synthesizes maps using the NACO style based on data from each country's Aeronautical Information Publication (AIP). This will not match what local charts look like and is not valid for navigation. Within the US, you can select individual charts by name or the "World" layers that do a clever panoramic blend of all available charts into one seamless worldwide chart.
The "Lo" and "Hi" charts refer to the NACO  "IFR En-Route Low" and "IFR En-Route High" charts. These are roughly equivalent to NACO VFR sectional charts. NACO "IFR Area" charts (only available in a few areas) are roughly equivalent to NACO VFR Terminal charts.
You should look at the NACO chart legends for a full explanation of what all the symbols and numbers mean, but for example, the number above the airway label (without a * or G prefix) is the Minimum En-Route Altitude (MEA), which provides both terrain and obstacle clearance and navaid radio reception. The number below is the length between waypoints in nautical miles.
The NACO "Low" charts show airways with an MEA below FL180, which have labels beginning with V or T, and NACO "High" charts show airways with an MEA of FL180 or higher, which have labels beginning with J or Q. Most other countries use the ICAO naming scheme where all "Upper" airways have a "U" prefix plus some other letter, though what "Upper" means varies by country. Skyvector tends to put "U" airways on the "World Hi" chart and all others on the "World Lo" chart, but it's not consistent across countries, so they may be using other data as well.

This much depends on where you are. Generally speaking, airways are no longer VFR, but IFR. For most sectors, there is a minimum height in the charts - generally speaking, they must be in controlled airspace, but also terrain will have its impact... Plus on all airways, there are limits to maximum and minimum altitude - and this will result in what charts they are shown...

I am speaking for europe or specific Germany right now. Using skyvector I see all the airways with their names and directions. But what are all these numbers over and under the airways names? For sure they are not the bearing, but aso not height I guess.

Is there any site I still miss that explains that? I mostly can read Airport Charts ... but not this skyvector map :-/


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Why do airfoils in an airplane's wings have different shape and size along its span?
Why wings of an airplane consist of different shape and size of airfoil. What will happen if the thickness of wing are same throughout the wing?

I fail to understand if you think the airfoil profile is the same along the span or if it differ (the eta seems to have different profile (namely HQR1, HQR2 and HQ17))

If the airfoil profile does not change along the span, then we can expect the entire wing to enter a stall condition at the same time. This means the stall break will be sudden and sharp.
If instead we transition between several different airfoil profiles along the span of the wing, we can get different portions of the wing to stall at different airspeeds/angles of attack/load factors, rendering the stall more gradual and furnishing the pilot with warning that the stalling process has begun.
Furthermore, if we profile the wing so the wing root begins to stall first while the wing tip is still flying, then we can reduce the tendency of an incipient stall to roll the plane and also maintain aileron authority and hence roll controllability longer into the stall than if the wingtip and the aileron stalled first.

"If the airfoil profile does not change along the span, then we can expect the entire wing to enter a stall condition at the same time" I don't think this is a sufficient condition for simultaneous stall, without a qualifying statement about the induced angle distribution.

"What would happen if the thickness...are same throughout the wing".
This is known as a "Hershey bar" wing, and is an excellent general purpose, easy to build wing for models and full scale aviation aircraft alike.
Aircraft designers add twist or "washout" to wings to prevent the entire wing from stalling at once.  Washout lowers the angle of attack of the wingtips a few degrees as compared with the wing roots. That, along with inboard flaps (near the roots), helps insure that the stalled airflow condition starts near the roots, rather than near the wing tips.
Tapered wings of varying thickness came along in the 1930s to deal with increased (wing) spanwise stress loads of larger and faster aircraft, and are particularly valuable in efforts to increase roll rate and reduce drag, hence they are seen in long distance cruising aircraft today such as gliders and airliners.  Leading edge slats make these wings much safer, but they are more complex and expensive to build.
The simple, reliable, lower aspect rectangular wing form, set high with a little dihedral as seen on the Cessna 172, remains a good choice for a recreational aircraft.


text:
Does angular momentum contributes in lifting a helicopter?
I want to know whether it is possible to make a helicopter with blades that rotate counter-clockwise (CCW) seen from below. I have difficulty understanding the angular momentum in this situation.
As we may see in the picture below, the rotor rotates clockwise (CW) seen from the pilot seat look up. So far, the rotations I have seen. To extend this question: is it possible for a single engine airplane to have propeller rotating counter-clockwise (CCW) seen from the rear, looking in the direction of the nose (as so far, what I found is that every single engine airplane is rotating CW). As we know from physics, the angular momentum of a CW helicopter will be pointing up, and the angular momentum of a single engine with CW rotation is pointing forward. To be clearer: Is there any impact (i.e. power efficiency, etc) if a helicopter's blades rotate CCW (seen from below), or if a single engine plane's propellers rotate CCW? Of course their torques will be different, but it is not the case in my question as long as it is not affecting the performance (i.e. reduce the power efficiency, etc).

Picture source: Picture 1, Picture 2;

Note that angular momentum is not a force.

I do not understand the question.

@Bianfable, I understand that it is not a force. If it is a force, then will no question. But however, it is a vector.

Related. Props turn CW in most single-engine American aircraft, but Russian and Chinese ones often turn CCW. I'm not sure why you think it would make any difference.

@AirCraftLover vectors are just mathematical means to represent a physical value. For speed (or forces), we use vectors; for rotation (or torque) we also use vectors. speed, force, rotation and torques are not a vectors, but we usually use vectors to represent them.

@ManuH Speed is a directionless quantity and is not a vector, but velocity is. Force is a proper vector, while torque and rotation are technically pseudovectors.

Well, angular momentum I·w is the rotating-motion equivalent to linear momentum m·v. Both are vectorial magnitudes.

@NuclearWang No, they are not vectors. They are physical values. Vectors are just a tool to represent them.

@AirCraftLover, in a sense the angular momentum is actually a bivector, a result of external product of two vectors describing an oriented plane. Just because in 3-dimensional space that looks just like a vector, it is considered one, specifically the normal vector of the plane. It is produced by the cross-product, which is defined exactly like external product, but using the normal base of $(x, y, z)$ instead of bivector base of $(yz, xz, zy)$. But in any other number of dimensions, angular velocity and angular momentum are not vectors.

@Pondlife, if you don't mind, can you please show me the video of a helicopter or a single engine airplane which their rotor rotate CCW? I appreciate if may. Just to ensure myself that is the angular momentum is not affecting the lifting force.

@ManuH, the direction is absolutely important in physic. The direction is a differentiating thing from scalar. There we will know where the force will go.

You might not be aware that nearly half of the helicopters have the opposite rortor rotation; but you surely know that there are multi-rotor and co-axial helicopters, and they always have counter-rotating rotors?

@AirCraftLover I fail to understand your point. My point is that mathematical tools used to work with a model are not the physical objects they represents but a representation and only one representation for one possible model. Thus you cannot say "a force is a vector" but you can say "you can represent a force by a vector in Newtonian mechanics"

Well helicopters are designed with both types of rotor systems.  American built helicopters have main rotors which rotate counter clockwise whereas European built helos have clockwise turning rotor systems.  Near as I know there is no particular advantage to one over the other, though you do have to reverse anti torque pedal corrections for collective inputs on a CW turning rotor system vs a CCW system, transverse flow effects are reversed and LTE events are more likely from right vs left crosswinds.
Just to be clear, torque is VISUALIZED as a vector perpendicular to the plane of rotation; it is not a force.  If the latter were true, you could propel craft to the moon and beyond using just a gyroscope.

Force is a vector, but not all vectors are forces. Vectors that are not forces include:

Torque
Linear momentum
Angular momentum
Velocity
Displacement
Electric field strength
Vorticity

and many many many more.
Some of them may be kinematically/dynamically coupled to forces, or may produce forces via aerodynamic means (e.g. linear momentum through fluid creates aerodynamic forces). But they are still not forces; You can't simply add them up.

In an inertial frame of reference, with a balanced propeller, there is no fore or aft forces except for the aerodynamic forces, so it will  not make any difference if it is a left handed or right handed prop.
Some very strange effects come into play though when you are not in an inertial frame of reference though, if you have a bicycle wheel lying around, hold the axle steady and spin it, you should feel no forces. Now try repeating this while moving around... The forces you feel are sometimes referred to are a result of something with angular momentum moving in a non-inertial frame of reference. In a constantly rotating frame of reference, you have the coriolis and centripetal 'fictitious' forces. When there is acceleration, it gets even more complicated (Eular force).
Given the coriolis effect from the earth's rotation on the scale of a rotating propeller is so small, it is fine to completely disregard it, however there is a tiny difference in forces depending on which direction you are flying.

Is there any difference in forces? I don't think angular momentum can produce forces, just torques (and there is no fixed point pivot off). Note that linear and anguar momentum are both conserved, but each on its own.

Correct. Angular momentum can only produce torques when it is changed (Newtons second law applied to rotation). The other body forces that arise from non-inertial reference frames (centripetal, coriolis & Eular) can be considered as fields with a resultant force that acts on the objects COG.

@StuartBuckingham, maybe I am not clever enough to express my aim. Just allow me to ask another question but still related: Will any different if a helicopter or a single engine propeller rotate CCW? Different here, means, CW will be better (or probably also worse) from CCW.

@AirCraftLover - As stated by others, here are plenty of airplanes and helicopters that have props and rotors rotating in either direction. There are even aircraft with multiple props and rotors rotating in opposite directions on the same aircraft. Except for clearance issues and counteracting unwanted gyroscopic effects (especially during the loss of an engine), there is no advantage of CW vs CCW. Which one is chosen is more out of convention and the simplification of the fabrication, repair, and maintenance logistical supply chain than anything else. Interchangeability has value.

As we know from physics, the angular momentum of a CW helicopter will be pointing up

No, you have completely misinterpreted what the thumb is in your right hand rule diagram is and have put more stock into its physicality than there is. If we wanted to we could use the lefthand convention instead of the right hand convention in our math instead. Would you be asking if the lift is decreased from the angular momentum in that case?
The upward pointing thumb is just a mathematical definition we use for convenience since it allows us to uniquely define the direction and orientation of rotation in 3D space with just three numbers (one vector) instead of many, many more. By this, I mean that the other way to represent angular velocity is a set of linear velocity vectors all pointing tangentially to the rotation equidistant from the axis of rotation such that translation/linear motions cancels out. That's difficult to work with mathematically and doesn't provide any more unique of a definition of direction than the right or lefthand rule does. That math has then been arranged such that using that convention produces results that make sense in the real world.
What you are doing is a bit like writing down the number 5 to record that there are 5 apples, but then thinking that number 5 is the apples.

Clockwise versus counter-clockwise propellers and rotors are nearly irrelevant. They don’t matter to the performance of the aircraft. They only matter in a difference in flying technique. The Angular Momentum does not contribute to lift in a helicopter nor thrust in an airplane.
The site you reference in your question does not present any force of lift. There is no force implied acting parallel to the plane of motion of a spinning object. Neither the L (angular momentum) nor the omega (angular velocity) produce a force that will act upon an object outside of its frame of reference. In other words, they will not lift a helicopter nor push/pull an airplane. Don’t let the L fool you into thinking that it stands for Lift. It does not.
Take the weighted bicycle wheel attached to handles experiment as an example. Once you start the wheel rotating in open space, its angular momentum will want to keep its position (or at least direction) rigid in space. As long as you keep the handles pointed in a consistent direction, the spinning wheel will provide no force until it makes contact with some surface (torque). The wheel will not push nor pull the person or object holding it. Only if you apply force to change the position of the wheel’s axis (the delta in the equations), will the wheel apply a force to remain rigid in space. Or, it will transfer the force in a direction according to the direction of its spin (gyroscopic precession).
In real world application, this means that you can ride a bicycle without worrying about a force pulling you to one side or another. It is actually easier to balance staying upright the faster the wheels are rotating. You can even ride with no hands touching the bicycle. And, when you do want to turn the wheels, all you have to do is lean to one side or the other. Gyroscopic precession will turn the wheels for you.
Another example is how motorcyclists can stay upright without much motion forward. They rev the engine while engaging the clutch while relatively motionless or at extremely low groundspeeds. Revving the engine spins the flywheel attached to the crankshaft. The flywheel acts like a gyroscope. Again, this provides rigidity in space. It does not matter which direction the motor spins. All that matters is the rotational and angular velocity of the flywheel and the flywheel’s mass.
So, yes both clockwise and counter-clockwise engine-propeller/rotor combinations exist in aviation. The only advantages of one over the other is logistics, not performance.


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Why are traditional knobs not replaced by touchscreens in cockpits?
Looking at this picture of an A380 cockpit I see that there are still a lot of traditional switches (meaning manual click on and off or knobs). Being technology so advanced in these days, why is it that traditional switches and knobs are used instead of having a couple of touch screens on which the various controls are placed?
Wouldn't this make it more economic as there would be savings on material and wiring? They could also be less susceptible to failures as traditional switches and knobs still rely on mechanical actions.
Another advantage I could think of is that every pilot could customise positioning of controls and switches based on his/her way of piloting. This could then be reset to a default state every time a new pilot takes over.

Just look at the big mess all home equipment is now. You never know how to use it without opening the manual, or you keep clicking 23 times like a mentally ill just to change from summer time to winter time, and you are lucky if you manage to stop clicking before being too far :(

As for any electrical systems, you should think of what happen in case of (partial or total) electrical failure. Also note that for home devices, keyboard are easier and faster to use than touch screen for many usages (e.g. post on this website)

Closely related

@mins There are many manuals, and you'd never know how to use a modern commercial jetliner without years of training and studying of many types of reading material.

If electricity where to die out on the aircraft for whatever reason the screens would shut off, so you would still want those switches just in case of that kind of situation. That's just my thoughts on it though.

@ToddWilcox: But in a B737, at least when you want to change the bank angle limit you don't have to remember that it buried in the configuration -> current flight -> FMS ->other -> angles -> bank -> max option.

Already covered over on UX.se.

"every pilot could customise positioning of controls" There are some fairly good reasons for the control layout to be fixed. Any pilot who is qualified on the aircraft should be able to sit down and know where everything is. No "reset to default" methods, no software glitches getting you stuck on the last pilot's weird settings, no accidentally moving an important function to somewhere unhelpful (or removing it entirely?) - particularly if you don't realise you've moved/removed the function until you need it in flight.

You must look at what your hand when using a touch screen in order to get the correct spot. With a mechanical control, muscle memory will get your hand to the right spot, and the control shape (for major controls), will confirm that you're there, all without ever looking in the cockpit. For example, I can find the power button on the TV remote without looking at all, while using my phone as a remote for Kodi requires that I look at my phone - if I drag my hand looking for the pause button, I'll hit all sorts of other stuff.

"They could also be less susceptible to failures as traditional switches and knobs still rely on mechanical actions."  As someone who designs devices using both touchscreens and physical buttons, all I can say about this is no.

I'm not a pilot, but I have worked in recording studios which could possibly be the only place where a person is surrounded by more knobs, switches, sliders and indicators than a cockpit. Smaller studios have largely switched to digital workstations where all of the controls are on a computer screen. There are a lot of advantages, but anyone who does a lot of serious work with them will eventually break down and buy an interface so that all of the virtual knobs and sliders are controlled by physical ones. Touch screens just don't create the tactile feedback the human brain works so well with.

@TomMcW: Makes sense to me too. We have 2 hands and 10 fingers, using a touch screen is a waste of human physical capabilities. Using a mouse is already a problem, most well trained computer users replace the mouse by keyboard shortcuts that are faster (e.g. Ctrl-C Ctrl-V). Forcing such users to use only the mouse or the finger and the Edit menu creates an important frustration. This is what is happening today with tablets.

"every pilot could customise positioning of controls and switches based on his/her way of piloting". This is sort of done by the Multi-function display, but it isn't about pilot customization. It's about saving space in small (ie. military) cockpits where space is at a premium. It also allows you to add new capabilities to the aircraft without having to redesign the cockpit. The downside is you have a bunch of similarly shaped buttons whose function changes with each mode.

Have you ever tried using a large touch screen during violent turbulence? Try drawing a straight line on paper while sitting in a vibrating chair on max, only the paper is glass and even the slightest touch is a command issued

Note that the Dragon 2 spaceship will in fact have mostly touchscreens for controls. However, the ship is almost fully autonomous, they are to be launched, controlled, docked (or birthed, I'm not sure), and landed roboticly much as the unmanned Dragon is.

The Russian Ka-62 helicopter has been shown equipped with a touch-screen 'glass cockpit'. Innovative technology might be more acceptable in the applications it is aimed at ("..cargo transportation, medevac and search and rescue operations, and can also be used in the oil and gas sector and for corporate purposes") than it would be in an airliner.

"every pilot could customise positioning of controls and switches based on his/her way of piloting" Wow, what could possibly go wrong?

@mins: I think we can do without spreading disgusting stereotypes about those with mental disadvantages, thank you.

Note: the Garmin G3000 which is mainly geared toward the smaller turbine side planes is already incorporating touch screens.

@mins: The well trained computer users use things like e.g. Vim, exactly for the reasons you mentioned: Keeping your hands on the keyboard where every movement carries so much more, and more precise, information.

OP have you ever tried to use toutchscreen keyboard?

@LightnessRacesinOrbit Think of it another way: what could possibly go wrong if a switch is left in the wrong position?

@sanchises: I don't see the relevance of that. Misconfigurations can happen with either technology: that's not unique to either, and therefore not a selling point in either one's favour.

@LightnessRacesinOrbit Exactly my point - "what could possibly go wrong" goes for both options. Although indeed, I can only begin to imagine what happens when you accidentally load the wrong savefile...

I support iPads as electronic flight bags (don't ask, or do!).  The problem I currently face is that the passcode requirement for email locks a device that is needed to reference charts, etc. on approach.  I've got a solution, but I can imagine this is compounded for actual flight instruments.  Tactile controls all the way.

Adding a pilot's perspective to what others have said:
Look at the switches and knobs in an airplane up close some time. You'll notice that nearly all of them have different textures,heights,sizes or shapes. That's intentional. Pilots train and train and train and train on checklists, especially the emergency ones. Muscle memory is a big part of quickly and correctly executing an emergency checklist.
As an example, flap levers/switches normally have a cap or top that is flat and parallel to the wings. It's easy to identify solely by touch.
Checklist item: "flaps up"
Action: Hand to flap lever (automatic after doing it a hundred times in training), verify feel of lever, move, look to verify
Without the tactile element, every motion would have to be verified by looking before it's made. With the tactile element, the movement can be made and then verified visually while the hand is moving to the next item. In an emergency, every second counts and the savings from tactile + verify matters.
Beyond emergency procedures, they're simply safer. The plane I fly the most has a touch screen display and several non touch devices. In turbulence, the touch screen is basically useless. But, the important devices all have buttons and knobs. I can be banging my head on the ceiling (literally) and still adjust the auto-pilot or radio. In that kind of turbulence, the touch screen device is completely useless.

This. 100% exactly! Try tuning the touch-screen radio in your car on a bumpy road. Now try it with a knob. No contest!

Ha, I just made the same comment above before scrolling down and reading this answer. I think the turbulence answer should be the #1 canonical answer; the rest of the answers here are all true, but the human factors seem like the primary reason physical controls persist.

@egid perhaps I'm just interpreting it differently, but I'd consider turbulence an environmental factor, not a human factor (to me, "human factor" = "human error"). While humans are involved in the error that'd be introduced by turbulence, it's not directly their fault.

@DoktorJ Well, Human Factors as a concept is the study of the interaction between man & machine. Turbulence is environmental, but it affects how effective we are at manipulating the controls and is certainly something that guides cockpit/flight-deck design.

Welcome Sean, nice first post! Hope to see more of those.

Adding to the absolutely correct answer of @Mach1:

Flicking a switch gives clear haptic and audible feedback. Compare that to a touchscreen where you can never be sure if your intention has been interpreted correctly. This might not seem to matter much, but if you need to throw 20 switches in a hurry, the mechanical solution is head and shoulders above anything with a touch input.
Mechanical switches can be operated with gloves on. Touchscreens generally cannot.
If the computer driving the touchscreen crashes, you are out of control. Mechanical switches don't have this failure mode.
Mechanical switches are far easier to debug than touchscreens. You can make sure if the switch works by using a screwdriver and a voltmeter. And some knowledge of the routing, admittedly.

@Greg Taylor and @Lightsider are correct: Inadvertently flicking a mechanical switch is so much harder than one on a touchscreen, especially if it has a cage to protect it from movements in an off direction.

Toggle switch with cage (picture source)

I'd add one small point, that inadvertently hitting a switch with a touchscreen would be far more likely. Brushing another area of the screen with a pinky or knuckle could change something you didn't intend. A physical switch doesn't change from such a light touch.

Especially if you're operating the aircraft in heavy turbulence!

@GregTaylor: Right, and for that reason important switches have cages around them so they need to be toggled by a movement in the right direction.

As anyone who has driven a car for several years knows, once you are familiar enough with physical controls, you can keep your eyes on the road (or skies, or display, or altimeter, or whatever) and 100% use touch to find, check the current setting of, and change the setting of a physical control. Not so with a touchscreen control.

I think the point @ToddWilcox makes deserves more visibility than a comment affords. I know it's a big reason for me to prefer physical controls in high-focus environments, even if those physical controls in the end change some setting in an electronic system (like the radio's volume level in my car, which uses a continually rotating knob to adjust the volume but provides clear tactile feedback that I am (a) touching the right control and (b) operating said control).

Touch-screens respond instantly when you touch them (except when they don't), while you can rest your finger/hand on a mechanical switch, prepared to activate it while not making any change. For example, the PF having his hand on the throttle levers on landing in case a go around is necessary. If that was a touch screen throttle - good luck.

@FreeMan I'm just imagining a touchscreen slider for the throttle suddenly jumping to TO/GA or idle because of spurious readings from the touch screen digitizer. shudders

There's also the fact that, with a mechanical switch, you can put your hand in the right, approximate area and find the switch by touch.  You don't HAVE TO look at the switch.  And if you're sufficiently familiar with the positions and what they mean, a simple touch will also tell you what position it's in without looking.  Many of the mechanical switches require that you pull the switch outward before you can move it.  So you're unlikely to inadvertently move them to a different position by touching them.

your third point is not really valid, people trust mechanical switches more, but I work on stuff like "the computer driving the touchscreen" and a lot more effort is put into making sure they don't crash than you  would want.

Don't forget turbulence. Have fun tapping in a frequency on a touchscreen in mod tb; I finished a minute ago with knobs. Just imagine driving on a washboard or gravel road, trying to use a touchscreen that's an arm's length in front of you.

@Sam You can put all the effort you want into making sure they don't crash... but any non-zero chance of failure is catastrophic if all your controls are in a single screen, and you can't tell me you can guarantee a zero chance of failure. Also, the operational environmental variables are infinite for all practical purposes, and designers can only test against and/or plan for a finite number of cases.

@Doktor J and you can say that mechanical linkages, electrical linkages and switches are test for all cases?

Further to @ToddWilcox's comment, when I got my current car I spent half an hour parked in the driveway practicing finding each control I might want to adjust while driving. If I cannot find and adjust a control by touch that control does not exist while I'm driving.

Mechanical switches gives a better visual inspection than digital touch screens. For a pilot surrounded with so many switches, just a visual glance would be enough to find the position of the control.

In addition to the vsual feedback, touching a knob without looking at it also provides a feedback on its position (I agree this is not enough to be sure the knob is in the correct position, but it is an information that can trigger some check process)

As an additional point, when using a touchscreen your hand is blocking the view of it.  You can't see the actual button that you are pushing, and you can't grab a switch, verify that it is correct, and then move it.

I wouldn't agree entirely with visual inspection. With a touchscreen, a good interaction designer can make visual inspection much easier. Besides, only the buttons which need to be shown at a time can be shown, thus reducing a LOT of visual clutter.

@Nav "only the buttons which need to be shown at a time can be shown" You mean, "only the buttons the interface designer assumed you'd need to be shown at a time can be shown."

@Nav "reducing a LOT of visual clutter" Is visual clutter in the cockpit a problem for properly trained pilots? I'll grant you it can be intimidating at first, but once you know the control layout, I tend to find "cluttered" panels easier to use in many situations because the control is always right there, in the same spot every time, no matter what else is going on.

Beyond the obvious aviation reasons of cost and so on, I can think of a few reasons why I'd not want an over reliance on touchscreens in the cockpit:

If a touchscreen fails, you've lost all the controls that were related to it.
Likewise, if a touchscreen (or portion of) fails then the whole thing has to be replaced rather than just the button
Feedback - phones and similar devices offer things like haptic feedback to register a positive touch. I can't imagine that being implemented and working well in a fixed monitor. Pressing a button provides a positive reinforcement that you did press the button.
Using touch-screens is hard if they're not still - it's far easier to press a physical button, without pressing an adjacent button, than it is to press an area on a screen without accidentally glancing another area.
Some controls are designed to be easy to operate, while being hard to do accidentally - for example flaps, gears, mixture etc. All of these require some positive force.

With that said - you've posted some advantages and, in honesty, I suspect it'll all happen one day. So, for that reason, in the meantime I give you the stock answer to any "Why isn't..." aviation question:

Cost
Certification
Proven reliability
Market demand

Unless pilots and airliners are crying out for it, and a manufacturers think it will make the difference between whether they buy a particular aircraft or not, they simply aren't going to spend the time and money necessary to make it a reality.
Additionally, it'll almost certainly come in slowly. It's one thing to add some touch functionality to a flight computer but I wouldn't be expecting flap and gear levers to be touch sensitive anytime soon!

For new designs, I'd actually guess that the touch screen solution would cost less, especially since modern glass cockpits already have plenty touchscreens in place (and a lot of controls already have been assimilated into these.) Reasons 3-5 have a lot more to do with why lots of other switches still exist, though, imo. (And reason 6: having a touch screen control for the main power bus doesn't work out well, since it becomes very hard to turn it back on without power...)

"Proven reliability" A big deal in aviation.

@reirab if you see a screen in a cockpit, don't jump to the conclusion that it is a touch screen. The downsides of a touch control do not carry over to displays so you might be noticing that instead of physical dials, a cockpit has multi-function displays. I would bet that what controls the display are traditional knobs / levers / buttons though.

@KellyS.French Yes, sorry, you're correct. That was a typo on my part. I meant to say "especially since modern glass cockpits already have plenty of screens in place." The point was that adding a touch-screen digitizer is not expensive (especially not relative to the cost of new aircraft.) Why touch screens aren't used for most of the controls has more to do with the other reasons listed here.

Touchscreen flight displays are already under production and the first commercial aircraft with touch screen primary flight displays as standard equipment to receive FAA certification is the Beechcraft King Air 250 turboprop equipped with Rockwell Collins Pro Line Fusion avionics.
There are some issues with touchscreen, such as,

...special security procedures are needed to avoid unintentional taps or movements that could jeopardise flight safety, especially during turbulence.

However, touch screens for aircraft are under intense development by almost all of the major avionics manufacturers and should be available for large aircraft by the end of the decade.
As an aside, the F-35 is the first combat aircraft to use a touch screen.

Very interesting. Would be nice to know what solutions are being explored to avoid unintentional taps.

@FabrizioMazzoni: I've heard that taps are ignored, and large directional swipes (think iPhone's "Slide to Unlock") are the safe way to design for touch-screen controls in the cockpit.

"Wouldn't this make it more economic as there would be savings on material and wiring?"
Not necessarily, because the days of "one wire per function" are long over.  Automotive has pushed that forward, and aerospace is following.  Modern systems tend to be networked. This actually gives better reliability for less wiring, because it's easier to duplicate individual network cables than to duplicate a 6"-wide bundle of wires carrying the same information.  Superficially the cockpit may still have 30-year-old switches and dials, but expecting 30-year-old wiring under the surface is generally incorrect.
"They could also be less susceptible to failures as traditional switches and knobs still rely on mechanical actions."
So do touchscreens to some extent.  As for numbers of failures, how robust is your phone screen to minor impacts, compared to the switches on your car dash?

"Automotive has pushed that forward, and aerospace os following." Really? Can-bus is older than Arinc 429?

Ive had touch devices misread my intentions many factors of factors times more often than mechanical switches. Furthermore you can operate mechanically arranged interfaces without looking, ie. by feel. In fact, having an interface that responds when you touch it is not at all what you want to happen when safety is a major concern.

When my hands are swatting, or there is dust in the air etc I find that the touch screen on my phone does not always work.   Also in turbulence, how well can someone touch a flat smooth screen in the correct location, but a physical 3d switch can still be used.  Also what if the operator has to wrap his/her hand in a cloth due to it bleeding?
Do you wish your life to depend on the above?
However on the ground, a touch screen make sense for reading of event logs etc by a maintenance person.

If the pilot's bleeding, I'm not sure I want him or her anywhere near the controls, thank you very much.

@LightnessRacesinOrbit Better a bleeding pilot than no pilot at all

@belisariushassettled: If your A380 only has one pilot then you have bigger problems.

@LightnessRacesinOrbit I know. But I still prefer that only bleeding pilot in the cockpit rather than away from it! :)

Don't try at home experiment:
Spill lots of water on a touch screen and try to use it.
Close your eyes and use your touch phone or tablet.
Try the same with knobs and switches.
Also, it is easier to specially and individually protect mechanical actuators against accidental manipulation than making hundreds of dedicated touch screens and protect those. It makes no sense if each knob/switch needs to be implemented as a dedicated touch screen, with a fallible control computer or some electronics behind it (in addition to the switching logic behind the knob or switch).

The A380's maiden flight was in 2005.
iPhone's release was in 2008.
Planes development cycles are drastically longer than phones, and require very reliable materials.
We just didn't had readily available large capacitive touch screen when engineers started designing the A380's cockpit.

But we did have resistive touchscreens, and the biggest advantage of capacitive is multi-touch, which is a whole extra layer of complexity.

Indeed. But Resistive touch screen are drastically less user friendly, precise , and convenient to use.

@ChrisH Capacitive touchscreens are truly touchscreens. Resistive touchscreens typically required some force: you had to actually press into the screen. Though that might actually be an advantage to prevent accidental touches... but it's also generally less accurate with a finger, and easier to accidentally break (thin plastic vs thick plastic/glass).

Nintendo DS are portable devices that use a resistive touchscreen along with a stylus. The device has very good response to touch, despite being resisitive. Also, I remember late-generation PDAs that had very good resisitive touchscreens too.

@Bob, I think you simply dealt with devices with low-quality resistive touchscreens.

Using a stylus to manipulate a screen is not very convenient ...

@Sleblanc, My Sony Z Xperia Ultra is both resistive and capacitive (in addition to being water proof). It works very well, but spill a drop of water  on it, or a drop of coffee, and it thinks the liquid is actually touching the screen.

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text:
Is the Morse code identifier required continuously when using a VHF NAVAID for navigation?
I am thinking of getting an MGL N16 VHF Nav radio with the MGL Vega V16 Control head. It has an interesting mode of operation (referred to as SCAN Mode) where the single receiver in the N16 rapidly switches back and forth between the primary and standby VHF frequencies. In this mode the Vega screen displays navigation information from both frequencies on the screen at the same time - (2 VORs, or a VOR and an ILS, for e.g.). Of course in this mode it is not on either frequency long enough to hear, or to decode the audible Morse code identifier, so the system does not send the audio to the intercom or display decoded ICAO call letters on the screen. With SCAN Mode off the Morse code from the one (primary) frequency is audible, and the screen shows the decoded 4-character identifier next to the frequency.
I was told (although I have not been able to locate a reference for this), that FARs require that you identify the Morse  code identifier to legally use a VHF NAVAID signal for navigation.
So, although it is simple to turn the SCAN function on and off, do you need to have the Morse code identifier continuously, throughout the entire approach, to legally use a NAVAID for navigation?  Or is it sufficient to do this once, on the initial portion of the approach, and then turn SCAN Mode on to concurrently monitor another NAVAID (like an airfield VOR while on an ILS approach)?

I was taught to continuously identify an NDB, because there is no other indication if the station is lost. A VOR or ILS will flag if the signal is lost, so I wasn't taught to continuously identify those.

I have never heard it required that you listen to the Morse code, must less continuously.  (I can't shut it off fast enough!)  I know it is at least a best practice to ID a navaid, but personally I think it's overrated in terms of risk reduction.  Really, what is the probability that a signal is broadcasting on the same frequency, in the same approximate location, putting out the same course info, that you might accidently lock onto because you failed to ID the code? I guess maybe I just don't understand well enough what specific scenario the practice is trying to prevent. Maybe a question?

I have not been able to find any clear Directive in the FARs myself. I was told this by someone on another forum.. They mention that this is required because sometimes, when VOR signal is out of service, being tested, or in error, the ident is used to signal this, so absence of an ident, or an inaccurate or "TEST" ident can be the only indication that the signal is unreliable.


text:
Is ADS-B required for flight under class B airspace but outside the Mode C veil?
In the U.S., can a non-ADS-B equipped aircraft legally fly under class-B airspace extensions that are outside of the 30nm Mode-C Veil circle?

I assumed that you're asking about the US and added the faa-regulations tag. When you ask about regulations please tell us which country or regulator you're asking about.

Yes, and thanks!

This question could be improved by adding a link to FAR 91.225 -- https://www.law.cornell.edu/cfr/text/14/91.225

This question could also be improved by deleting the word "extensions".  Use "shelves" or "airspaces" instead.  "Extensions" is confusing because there is a specific type of Class E airspace (and in a few examples, Class D airspace) that is called "Designated as an Extension" by the FAA.

Added graphic showing where this occurs in Phoenix. It also occurs east of LAX class B, just west of Chino, as shown in graphic from @JSCarry

You may fly without ADSB under the Class B or Class C shelf provided you remain outside of any Mode C veil.
§91.225 tells you where you cannot fly. It says you cannot fly within the lateral boundaries of the Class B or C airspace or above the airspace. It does not say anything about under the shelf.
Here is an example of one such area:

skyvector.com
You can fly under 2,700' below the Ontario Class C and in the small slice of Class B you can fly up to 8,000' if you stay away from the Class C.
Paul Bertorelli has a good explanation on YouTube. (Updated link.)

(d) After January 1, 2020, and unless otherwise authorized by ATC, no
  person may operate an aircraft in the following airspace unless the
  aircraft has equipment installed that meets the requirements in
  paragraph (b) of this section:
(1) Class B and Class C airspace areas;
(2) Except as provided for in paragraph (e) of this section, within 30
  nautical miles of an airport listed in appendix D, section 1 to this
  part from the surface upward to 10,000 feet MSL;
(3) Above the ceiling and within the lateral boundaries of a Class B
  or Class C airspace area designated for an airport upward to 10,000
  feet MSL;
4) Except as provided in paragraph (e) of this section, Class E
  airspace within the 48 contiguous states and the District of Columbia
  at and above 10,000 feet MSL, excluding the airspace at and below
  2,500 feet above the surface; and
(5) Class E airspace at and above 3,000 feet MSL over the Gulf of
  Mexico from the coastline of the United States out to 12 nautical
  miles.

14 CFR § 91.225

Comments are not for extended discussion; this conversation has been moved to chat.

This answer could be improved.  As it stands, it contradicts itself.  The sentence "It does not say anything about under the shelf." contradicts with the sentence "It says you cannot fly within the lateral boundaries of the Class B or C airspace or above the airspace.", because the airspace under the shelf is obviously "within the lateral boundaries" of the Class B or C airspace.

The question appears to be asking "Can a non-ADS-B-equipped aircraft legally fly under Class-B airspace shelves that are outside any 30nm Mode-C veil?"
Yes it can.
See FAR 91.225.  The only clause in FAR 91.225 that at first glance might suggest otherwise, is 91.225(d)(3), which states "(d) After January 1, 2020, and unless otherwise authorized by ATC, no person may operate an aircraft in the following airspace unless the aircraft has equipment installed that meets the requirements in paragraph (b) of this section: ... (3) Above the ceiling and within the lateral boundaries of a Class B or Class C airspace area designated for an airport upward to 10,000 feet MSL;"
The most logical interpretation of this clause is that it only pertains to airspace that is simultaneously above the ceiling and "within the lateral boundaries" of a Class B or Class C airspace area.  In other words, the airspace being described is all the airspace that lies directly above the ceiling of a Class B or Class C airspace area, up to 10,000' MSL.  (And note that flying directly above the ceiling of Class B or Class C airspace above 10,000' MSL without ADS-B-out is prohibited by the combined action of 91.225(d)(4) and 91.225(e)(2).)  Therefore the clause in question does not restrict flying directly below the floor of a shelf of a Class B or Class C airspace area.
It would be illogical to interpret this clause to be inclusive of all airspace below 10,000' MSL that is directly "above the ceiling" or "within the lateral boundaries" of a Class B or Class C airspace area, because in that case the "above the ceiling" phrase would be redundant and the clause would have exactly the same meaning if the phrase were simply deleted.  All airspace that is located directly above the ceiling of a Class B or Class C airspace area also lies "within the lateral boundaries" of that Class B or Class C airspace area.
Yet another interpretation of this clause might take the "above the ceiling" phrase to also include airspace that is higher than the ceiling of a nearby Class B or Class C airspace area, but displaced laterally rather than actually overlying that Class B or Class C airspace area.  Now if the clause is interpreted to include all the airspace that is "above the ceiling" of a Class B or Class C airspace or "within the lateral boundaries" of a Class B or Class C airspace area, flight beneath Class B or Class C shelves would be prohibited.  However, this interpretation is completely unfeasible because there would be no way to know how far from the edge of the Class B or Class C airspace the prohibition against flying "above the ceiling" should be considered to apply.
Note that if the aircraft in question has no engine-driven electrical system, then the 30-nm Mode C veil is no longer an issue.  In this case the answer given above would also apply to the portions of Class B or Class C shelves that lie within the 30-nm Mode C veil-- such an aircraft would be free to fly under those Class B or Class C shelves.
One final note-- if the aircraft in question has no engine-driven electrical system and no ADS-B-out, then operations conducted within the lateral boundaries of Class B or Class C airspace must be conducted below 10,000' MSL, due to FAR 91.225(e)(2), as explained in more detail in this related answer.  There is at least one instance (KSLC) where the floor of a Class B or Class C shelf is above 10,000' MSL, and thus an airplane with no engine-driven electrical system and no ADS-B-out could not legally fly all the way up to the floor of that shelf.  An aircraft with no ADS-B-out that does have an engine-driven electrical system must stay below 10,000 MSL in all airspace over the contiguous 48 states that is not below 2,500 AGL due to FAR 91.225(d)(4), and so it too could not legally fly all the way up to the floor of a Class B or Class C shelf above 10,000' MSL, at least if that shelf had a floor higher than 2500' AGL and was located within airspace over the lower 48 states, even if that shelf were outside of any 30-nm Mode C veil, which the above-mentioned shelf at KSLC is not.
Here is an A.S.E. answer that addresses a question that is somewhat similar what to what is being asked here, but specifically focussed on aircraft lacking an engine-driven electrical system: What additional airspace will be off-limits to an a/c w/ no elect. system or xponder under 91.225 (ADS-B) compared to under 91.215?

yes, I agree with you... But your second sentence, "§91.225 tells you where you cannot fly. It says you cannot fly within the lateral boundaries of the Class B or C airspace OR above the airspace.", uses the logical operator "OR" and this is where I think, your choice of wording can confuse... suggest you remove the OR and replace with a comma, or the word AND, and replace "above the airspace "with IN OR ABOVE the airspace"?

@CharlesBretana -- did you possibly intend to address this comment toward the other answer to this question, by JScarry?  You are quoting his words not mine.  However bear in mind that JSCarry apparently has a theory that FAA usage of the phrase "within the lateral boundaries of" somehow automatically excludes all airspace below the floor of said airspace-- for more on this, see the chat thread that ensued from the comments that were posted under his answer.


text:
What is the "true static pressure"?
What is true static pressure? How do we define it? Is it same as corrected static pressure for installation and errors?
ARINC 429P1-18 defines Static pressure as corrected and uncorrected where in few places I have heard this term "True static pressure".

A reference of where you've heard/seen this would be useful, as I'm not familiar with the term

Aviation and Aeronautical Engineering, Volume 6, Section "Altitude errors in Aerial Navigation".https://books.google.com/books?id=Lm9VAAAAYAAJ&pg=PA624&lpg=PA624&dq=true+static+pressure+in+aviation&source=bl&ots=rEvqiszJXj&sig=CTgrXQyV1pBRU8ql_d9vQGBSDLQ&hl=en&sa=X&ved=2ahUKEwjm-ZXI6pjfAhWq0FQKHWxtBJs4HhDoATAIegQIABAB#v=onepage&q=true%20static%20pressure%20in%20aviation&f=false

The text you linked to indicates that the "true static pressure" takes into consideration airspeed, position on the aircraft, and air density

And it also might be beneficial to note that the text is almost a century old, so some of the terminology and error values may be different than those used today

How is this different from static pressure we get from pitot static tube ? I have never heard this term before. I was working on flare guidance system and they are also using "true static pressure " for computational purpose. So what is this term and why are we using it ?

Its on label 171 from ADC ....

From what I can see, the "true" static pressure is the measured static pressure corrected for airspeed & position (Static Source Error Correction).
In my copy of ARINC 429 (May 2004) I don't see a label definition that fits this "true static pressure". Label 171 can be used for manufacturer defined data, so I would see if you can get a better answer from the manufacturer of your data source.


text:
What is the criteria for selecting BNR or BCD as data encoding in ARINC429
I was going through ARINC429 part1-18 and found all the labels that are defined along with transmission bit and data encoding. What is the criteria for choosing BNR or BCD for data encoding ? Why are some BNR while rest are BCD ?

The general ARINC guideline for publishing data is to publish both BCD and BNR values when both types are defined. That allows the receiver of the data decide which to use. If only one form exists, then that's the way it's coded. It ultimately comes down to what the ARINC committee decided made the most sense.
Typically, BNR coded data is used by computational functions -- things that process the data value and expect the greatest precision in the number. They don't really care whether the number is easily readable.
BCD coded data is typically used by display systems as pilots like to read decimal numbers the numbers can easily be scaled to a readable display, e.g. DME range in NM rounded to the nearest 0.1 NM or bearing to the nearest 1 degree.
BCD is also used in control panels where the data is discrete decimal data (radio frequencies) and the crew enters a decimal value.


text:
Is there a term for additional casing that extends above the main fuselage?
There is a Russian term for this, which doesn't sound like a Russian word, гаргрот (something like gargrote in latin letters) which Wikipedia page doesn't have links to other languages (save for Ukrainian). So I am curious, what could be an English or French term for this, if any? And also, what could be possible origin for the Russian term.
A good example is a "hump" that stayed on the back of Douglas A-4 Skyhawk until A-4H modification, where it was removed.

Or that red case on the Kh-58 Soviet anti-radiation missile

There is not a general term for this.
What it is called will likely vary depending on the size, placement, and purpose.  For example, a bump like this that is a part of an original design is likely to be given a more favorable name than something added later.
One term would be a 'blister'.  On the other hand, the F-16's conformal fuel tanks are called just that.
'Protuberance' is a term that applies to just about anything that is not a 'clean' part of the aircraft.  The dictionary definition says it is for things that stick out, but in practice it can include bumps and blisters, as well as antennae, bonding straps, gaps, seams, fasteners, cooling vents, exhaust, etc.  Pretty much anything that adds drag to an aircraft, but that is not a part of the ideal smooth shape.
It seems the Skyhawk hump was not included on early aircraft, and was added to later aircraft to carry additional avionics / electronics.  skyhawk.org is a great resource on the skyhawk.  On that page, they call it the 'hump back'.
The bump on the missile is there to run wires or pneumatic/hydraulic lines past the combustion chamber.  They usually connect the guidance system (in the front) with the actuators for the control system (in the back).  The combustion chamber of the solid rocket motor is a cylindrical pressure vessel and anything that pierces that is a big problem.

I have heard an A4 pilot call this a "camel back." Also included on the A4M.